The by-election to Mandi Lok Sabha seat would be held on June 23.
The model code of conduct has come into force with immediate effect, Chief Electoral Officer, Narinder Chauhan said.
The seat was vacated by Virbhadra Singh in January after he was elected to Himachal Pradesh Assembly and became Chief Minister.
Mandi Lok Sabha seat comprises of 17 assembly constituencies.
The seat was won three times by Virbhadra Singh in 1971, 1980 and 2009.
Pratibha Singh, wife of Chief Minister Virbhadra Singh, was elected in 2004.
While the BJP has shortlisted three candidates -- Ram Swaroop Sharma, Jai Ram Thakur and Ajay Rana -- for this seat, Pratibha Singh is likely the Congress candidate.
